Washing machine and control method thereof

ABSTRACT

Disclosed herein are a washing machine that detects the weight of laundry based on the displacement of a rotary tub and a control method thereof. The washing machine includes a rotary tub displaced according to the weight of laundry, at least one sensor module to detect the displacement of the rotary tub, and a controller to calculate the weight of the laundry according to the displacement of the rotary tub. The weight of the laundry is sensed according to the displacement of the rotary tub in which the laundry is directly placed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit of Korean Patent Application No. 10-2010-0021829, filed on Mar. 11, 2010 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.

BACKGROUND

1. Field

Embodiments of the disclosure relate to a washing machine that senses the weight of laundry and a control method thereof.

2. Description of the Related Art

Generally, a washing machine includes a water tub mounted in a housing to receive water containing a detergent, i.e., detergent water, a rotary tub rotatably mounted in the water tub to wash laundry, and a door hingedly coupled to the front of the housing to open and close an opening formed at the front of the housing. Laundry is put into the rotary tub through the opening of the housing, a predetermined amount of detergent water is supplied into the water tub, and the rotary tub is rotated to wash the laundry.

When a user selects a washing course, the weight of the laundry is sensed to decide the amount of wash water, wash water sufficient to wet the laundry is supplied into the water tub together with a detergent according to the decided amount of wash water, and the rotary tub is rotated to perform a washing cycle and a spin-drying cycle.

When the weight of the laundry is accurately sensed, the amount of water corresponding to the sensed weight of the laundry is supplied to wash the laundry. Consequently, the amount of water and power used is reduced, thereby reducing energy consumption.

In the related art, laundry in the rotary tub is used as an inertia load, and inertia is estimated to sense the weight of the laundry. For example, predetermined voltage is applied to a motor to accelerate the rotary tub, and inertia is estimated using change in voltage and velocity of the motor during acceleration of the rotary tub to sense the weight of the laundry.

In this method of sensing the weight of the laundry, a weight sensing error may occur according to voltage. Also, the weight of the laundry may not be accurately measured.

SUMMARY

It is an aspect of the embodiments to provide a washing machine that accurately measures the amount of laundry and a control method thereof.

Additional aspects of the embodiments will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the embodiments.

In accordance with one aspect of the embodiments, a washing machine includes a rotary tub displaced according to weight of laundry, at least one sensor module to detect displacement of the rotary tub, and a controller to calculate the weight of the laundry according to the displacement of the rotary tub.

The washing machine may further include a water tub in which the rotary tub is provided, and the sensor module may be mounted at a front upper end of the water tub inside the water tub.

The washing machine may further include a water tub in which the rotary tub is provided, and the sensor module may be mounted at a rear upper end of the water tub inside the water tub.

The sensor module may include a light source to irradiate light to the rotary tub and an image sensor to receive the irradiated light to sense an image.

The sensor module may further include an image processor to detect displacement of the rotary tub according to the image sensed by the image sensor.

The image sensor may sense images of one side of the rotary tub before and after laundry is put into the rotary tub, and the image processor may compare the sensed images to detect the displacement of the rotary tub.

The sensor module may include a plurality of sensor modules mounted at a water tub in which the rotary tub is provided, and the controller may average or sum displacements of the rotary tubs detected by the sensor modules to calculate the weight of the laundry.

The sensor module may include a light emitting part to irradiate light to the rotary tub and a light receiving part to receive light reflected from the rotary tub.

The sensor module may irradiate light to the rotary tub and receive light reflected from the rotary tub before and after the laundry is put into the rotary tub.

The controller may compare light amounts received before and after the laundry is put into the rotary tub to calculate the weight of the laundry.

The washing machine may further include a memory to store the weight of the laundry according to the displacement of the rotary tub, and the controller may receive information on the weight of the laundry according to the displacement of the rotary tub from the memory to calculate the weight of the laundry.

In accordance with another aspect of the embodiments, a control method of a washing machine includes irradiating light to a rotary tub which is displaced according to weight of laundry, receiving light reflected from the rotary tub to detect displacement of the rotary tub, and calculating the weight of the laundry according to the displacement of the rotary tub.

Irradiating light to a rotary tub which is displaced according to weight of laundry may include irradiating light to the rotary tub before and after the laundry is put into the rotary tub.

Receiving light reflected from the rotary tub to detect displacement of the rotary tub may include receiving light reflected from the rotary tub before and after the laundry is put into the rotary tub to detect images of the rotary tub and comparing the images of the rotary tub before and after the laundry is put into the rotary tub to detect the displacement of the rotary tub.

Receiving light reflected from the rotary tub to detect displacement of the rotary tub may include measuring light amounts reflected from the rotary tub before and after the laundry is put into the rotary tub and comparing the light amounts before and after the laundry is put into the rotary tub to detect the displacement of the rotary tub.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects of the embodiment will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

FIG. 1 is a side sectional view illustrating a washing machine according to an embodiment;

FIGS. 2A and 2B illustrate the operation of a sensor module to measure the displacement of a rotary tub according to an embodiment;

FIGS. 3A and 3B illustrate the operation of a sensor module to measure the displacement of the rotary tub according to another embodiment;

FIGS. 4A and 4B illustrate the operation of sensor modules to measure the displacement of the rotary tub according to another embodiment;

FIGS. 5A and 5B illustrate the operation of sensor modules to measure the displacement of the rotary tub according to a further embodiment;

FIG. 6 is a function block diagram illustrating sensing the weight of laundry in the washing machine according to an embodiment;

FIG. 7 is a function block diagram illustrating sensing the weight of laundry in the washing machine according to another embodiment;

FIG. 8 is a function block diagram illustrating sensing the weight of laundry in the washing machine according to another embodiment;

FIG. 9 is a function block diagram illustrating sensing the weight of laundry in the washing machine according to a further embodiment;

FIG. 10 is a control flow chart illustrating a method of measuring the displacement of the rotary tub to sense the weight of laundry according to an embodiment;

FIG. 11 is a control flow chart illustrating a method of measuring the amount of light reflected from the rotary tub to sense the weight of laundry according to an embodiment; and

FIG. 12 is a view illustrating the operation of an image sensor according to an embodiment.

DETAILED DESCRIPTION

Reference will now be made in detail to the embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout.

FIG. 1 is a side sectional view illustrating a drum washing machine according to an embodiment.

The drum washing machine includes a box-shaped housing 10 forming the external appearance thereof, a water tub 20 provided in the housing 10 to contain water, a cylindrical rotary tub 30 rotatably mounted in the water tub 20, the rotary tub 30 having through holes 31 through which water and air pass, and a drive motor 40 to transmit rotational force to the rotary tub 30 such that the rotary tub 30 is rotated to wash and spin-dry laundry in the rotary tub 30.

The water tub 20 and the rotary tub 30 are partially open at the front middle portions thereof to constitute inlet ports 20 a and 30 a through which laundry is put into or removed from the rotary tub 30. To the front of the housing 10 is hingedly coupled a door 50 to open and close the inlet ports 20 a and 30 a of the water tub 20 and the rotary tub 30. At the inner circumference of the rotary tub 30 are arranged lifters 32 at predetermined intervals. During rotation of the rotary tub 30 in alternating directions, the laundry is lifted and dropped by the lifters 32, by which the laundry is washed.

At the inside of the water tub 20 is mounted a sensor module 80 to measure displacement of the rotary tub 30. The displacement of the rotary tub 30 is changed depending upon the weight of laundry. The sensor module 80 directly measures the displacement of the rotary tub 30 or estimates the displacement of the rotary tub 30 based on light amount (intensity) or light pattern changed according to the displacement of the rotary tub 30 to determine the weight of laundry.

Although one sensor module 80 is mounted at the inside of the water tub 20 as shown in FIG. 1, a plurality of sensor modules 80 may be provided to accurately measure the displacement of the rotary tub 30. Hereinafter, a method of sensing the weight of laundry using the sensor module 80 will be described in detail.

FIGS. 2A and 2B illustrate the operation of a sensor module to measure the displacement of the rotary tub according to an embodiment. FIGS. 3A and 3B illustrate the operation of a sensor module to measure the displacement of the rotary tub according to another embodiment. FIGS. 4A and 4B illustrate the operation of sensor modules to measure the displacement of the rotary tub according to another embodiment. FIGS. 5A and 5B illustrate the operation of sensor modules to measure the displacement of the rotary tub according to a further embodiment.

FIG. 6 is a function block diagram illustrating sensing the weight of laundry in the washing machine according to an embodiment of the present invention. FIG. 7 is a function block diagram illustrating sensing the weight of laundry in the washing machine according to another embodiment. FIG. 8 is a function block diagram illustrating sensing the weight of laundry in the washing machine according to another embodiment. FIG. 9 is a function block diagram illustrating sensing the weight of laundry in the washing machine according to a further embodiment.

Referring to FIGS. 2A and 2B, the sensor module 80 may be mounted at the front upper end of the water tub 20 inside the water tub 20 to detect the displacement of the rotary tub 30. In FIG. 2A, no laundry is put into the rotary tub 30. In FIG. 2B, laundry is put into the rotary tub 30. When laundry is put into the rotary tub 30, the rotary tub 30 is displaced. The displacement of the rotary tub 30 is proportional to the weight of the laundry put into the rotary tub 30.

The sensor module 80 measures the displacement of the rotary tub 30. Referring to FIG. 6, the sensor module 80 may include a light source 81, an image sensor 82 and an image processor 83.

The light source 81 may be composed of a light emitting diode or a laser. The light source 81 irradiates light to one side of the rotary tub 30.

The image sensor 82 receives the light reflected from the rotary tub 30 to detect an image of a pattern attached on the rotary tub 30. It is understood that a pattern may be printed on a rotary tube 30. However, it is not limited thereto. The image sensor 82 may include at least one charge coupled device (CCD) or complementary metal oxide semiconductor (CMOS) sensor. The image sensor 82 may detect a two-dimensional image of image pattern attached on the one side of the rotary tub 30 (a three-dimensional image may also be created).

The image processor 83 calculates displacement between two images using a correlation algorithm to compare the two images. The image processor 83 compares a current image with a reference image of one side of the rotary tub 30 to calculate image displacement. The reference image is an image of one side of the rotary tub 30 measured by the image sensor 82 when no laundry is in the rotary tub 30. The current image is an image of one side of the rotary tub 30 measured by the image sensor 82 when laundry is in the rotary tub 30. The operation of the image sensor will be described with reference to FIG. 12. The image processor 83 sets an arbitrary window, i.e., a mask window (for example, a window of 4×4 pixels), within the reference image (for example, an image of 12×12 pixels) and moves the mask window with respect to the entirety of the current image (for example, an image of 12×12 pixels) by an arbitrary pixel unit (for example, one pixel) to determine a correlation coefficient value (a value indicating image correlation). The image processor 83 performs comparison between the mask window and first to N regions of the current image to determine correlation coefficient values. The image processor 83 creates X-axis and Y-axis displacement values at the position having the largest correlation coefficient value. X-axis and Y-axis displacement values are values indicating the difference between the coordinate values (for example, the upper left coordinate values) of the mask window of the reference image when no laundry is in the rotary tub 30 and the coordinate values (for example, the upper left coordinate values) of the mask window, at the position having the largest correlation coefficient value, of the current image when the laundry is in the rotary tub 30. The X-axis and Y-axis displacement values indicate the displacement of the rotary tub 30. Information on the displacement of the rotary tub 30 is provided to a controller 100, which uses the displacement of the rotary tub 30 to detect the weight of laundry.

Although the image processor 83 is included in the sensor module 80 as shown in FIG. 6, the image processor 83 may be excluded from the sensor module 80, and the controller 100 may function as the image processor 83.

Referring to FIG. 7, the sensor module 80 may include a light emitting part 84 to irradiate light and a light receiving part 85 to receive the light irradiated from the light emitting part 84.

The light emitting part 84 and the light receiving part 85 are mounted to the inside of the water tub 20 to irradiate light to the rotary tub 30 and receive the light reflected from the rotary tub 30, respectively. The sensor module 80 transmits information on the amount (or intensity) of light reflected from the rotary tub 30 when no laundry is in the rotary tub 30 and information on the amount of light reflected from the rotary tub 30 when laundry is in the rotary tub 30 to the controller 100. The controller 100 communicates with the sensor module 80 to receive information on the light amounts, to detect the displacement of the rotary tub 30 corresponding to the difference between the light amounts and to retrieve the weight of laundry corresponding to the detected displacement of the rotary tub 30 from a memory 110 to determine the weight of the laundry.

Referring to FIGS. 3A and 3B, the sensor module 80 may be mounted at the rear end of the water tub 20 inside the water tub 20 to detect the displacement of the rotary tub 30. In FIG. 3A, no laundry is put into the rotary tub 30. In FIG. 3B, laundry is put into the rotary tub 30. A method of calculating the weight of laundry put into the rotary tub 30 is performed in the same manner as in FIGS. 2A and 2B.

Referring to FIGS. 4A and 4B, sensor modules 80 a and 80 b may be mounted respectively at the front upper end of the water tub 20 and the rear end of the water tub 20 inside the water tub 20 to detect the displacement of the rotary tub 30. Referring to FIG. 8, the controller 100 may combine displacements of the rotary tub 30 measured by the sensor modules 80 a and 80 b to sense the weight of laundry. The displacements of the rotary tub 30 may be combined, for example, using a method of averaging the displacements of the rotary tub 30 and a method of summing the displacements of the rotary tub 30.

The controller 100 may average the displacements of the rotary tub 30 measured by the sensor modules 80 a and 80 b to sense the weight of laundry. For example, on the assumption that the displacement of the rotary tub 30 measured by the sensor module 80 a mounted at the front upper end of the water tub 20 inside the water tub 20 is about 3 cm and the displacement of the rotary tub 30 measured by the sensor module 80 b mounted at the rear end of the water tub 20 inside the water tub 20 is about 1 cm, the controller 100 calculates the average displacement of the rotary tub 30, i.e., about 2 cm, and retrieves the weight of laundry corresponding to the calculated average displacement of the rotary tub 30, i.e., about 2 cm, from the memory 110 to determine the weight of the laundry. The weight of laundry corresponding to the average displacement of the rotary tub 30 may be preset through experimentation.

The controller 100 may sum the displacements of the rotary tub 30 measured by the sensor modules 80 a and 80 b to sense the weight of laundry. For example, on the assumption that the displacement of the rotary tub 30 measured by the sensor module 80 a mounted at the front upper end of the water tub 20 inside the water tub 20 is about 3 cm and the displacement of the rotary tub 30 measured by the sensor module 80 b mounted at the rear end of the water tub 20 inside the water tub 20 is about 1 cm, the controller 100 calculates the sum of the displacements of the rotary tub 30, i.e., about 4 cm, and retrieves the weight of laundry corresponding to the summed displacement of the rotary tub 30, i.e., about 4 cm, from the memory 110 to determine the weight of the laundry. The weight of laundry corresponding to the summed displacement of the rotary tub 30, i.e., about 4 cm, is previously stored in the memory 110.

In FIG. 8, light sources included in the sensor modules 80 a and 80 b are denoted by reference numerals 81 a and 81 b, image sensors included in the sensor modules 80 a and 80 b are denoted by reference numerals 82 a and 82 b, and image processors included in the sensor modules 80 a and 80 b are denoted by reference numerals 83 a and 83 b.

Referring to FIG. 9, the controller 100 may combine light amount changes measured by the sensor modules 80 a and 80 b to sense the weight of laundry. The light amount changes may be combined, for example, using a method of averaging the light amount changes to calculate the displacement of the rotary tub and sensing the weight of laundry based on the calculated displacement of the rotary tub and a method of summing the light amount changes to calculate the displacement of the rotary tub and sensing the weight of laundry based on the calculated displacement of the rotary tub.

The controller 100 may average the light amount changes measured by the sensor modules 80 a and 80 b to sense the weight of laundry. For example, on the assumption that the light amount change measured by the sensor module 80 a mounted at the front upper end of the water tub 20 inside the water tub 20 is about 3 lx (lux) and the light amount change measured by the sensor module 80 b mounted at the rear end of the water tub 20 inside the water tub 20 is about 1 lx, the controller 100 calculates the average light amount change, i.e., about 2 lx, and calculates the displacement of the rotary tub 30 corresponding to the average light amount change, i.e., about 2 lx. The controller 100 retrieves the weight of laundry corresponding to the calculated displacement of the rotary tub 30 from the memory 110 to determine the weight of the laundry. The displacement of the rotary tub 30 corresponding to the average light amount change may be preset through experimentation.

The controller 100 may sum the light amount changes measured by the sensor modules 80 a and 80 b to sense the weight of laundry. For example, on the assumption that the light amount change measured by the sensor module 80 a mounted at the front upper end of the water tub 20 inside the water tub 20 is about 3 lx and the light amount change measured by the sensor module 80 b mounted at the rear end of the water tub 20 inside the water tub 20 is about 1 lx, the controller 100 calculates the sum of the light amount changes, i.e., about 4 lx, and calculates the displacement of the rotary tub 30 corresponding to the summed light amount change, i.e., about 4 lx. The controller 100 retrieves the weight of laundry corresponding to the calculated displacement of the rotary tub 30 from the memory 110 to determine the weight of the laundry. The displacement of the rotary tub 30 corresponding to the summed light amount change may be preset through experimentation.

Meanwhile, the displacement of the rotary tub corresponding to the average light amount change or the summed light amount change is a relative value indicating the average displacement of the rotary tub 30 (average of the displacements at the front and rear ends of the rotary tub) or the summed displacement of the rotary tub 30 (sum of the displacements at the front and rear ends of the rotary tub), which is used to calculate the weight of laundry.

In FIG. 9, light emitting parts included in the sensor modules 80 a and 80 b are denoted by reference numerals 84 a and 84 b, respectively and light receiving parts included in the sensor modules 80 a and 80 b are denoted by reference numerals 85 a and 85 b, respectively.

Referring to FIGS. 5A and 5B, both the rotary tub 30 and the water tub 20 are displaced after laundry is put into the rotary tub 30 (FIG. 5B) as compared with before laundry is put into the rotary tub 30 (FIG. 5A). When the amount of laundry put into the rotary tub 30 is small, the rotary tub 30 may be displaced but the water tub 20 may not be displaced, as shown in FIGS. 4A and 4B. On the other hand, when the amount of laundry put into the rotary tub 30 is large, both the rotary tub 30 and the water tub 20 are displaced, as shown in FIGS. 5A and 5B (both the rotary tub 30 and the water tub 20 may be displaced irrespective of the weight of laundry). However, even when both the rotary tub 30 and the water tub 20 are displaced depending upon the amount of laundry put into the rotary tub 30, the same method as the method of sensing the weight of laundry described with reference to FIGS. 4A and 4B may be used to sense the weight of laundry.

Specifically, in the embodiment of FIGS. 5A and 5B, the weight of laundry is stored considering the displacement of the water tub 20 according to input of the laundry. In this case, a sensor is mounted at a frame of the washing machine to measure the displacement of the water tub 20 and to transmit the measured displacement of the water tub 20 to the controller.

For example, when the displacement of the water tub 20 measured by the sensor is about 1 cm and the displacement of the rotary tub 30 measured by the sensor module 80 is about 3 cm after a predetermined amount of laundry is put into the rotary tub 30, the real displacement of the rotary tub 30 is the sum of the displacement of the water tub 20 measured by the sensor and the displacement of the rotary tub 30 measured by the sensor module 80, i.e., about 4 cm (the water tub and the rotary tub are displaced in the same direction). That is, a designer may measure the displacement of the water tub 20 depending upon the weight of laundry to store the weight of laundry based on the real displacement of the rotary tub 30. Meanwhile, a method of sensing the weight of laundry based on light amount measured by the sensor module 80 according to another embodiment may store the weight of laundry based on the light amount in the memory considering the displacement of the water tub 20.

FIG. 10 is a control flow chart illustrating a method of measuring the displacement of the rotary tub to sense the weight of laundry according to an embodiment .

Before laundry is put into the rotary tub 30, the sensor module 80 irradiates light to the rotary tub 30 to create and store an image of one side of the rotary tub 30. When the light irradiated to the rotary tub 30 is reflected, the sensor module 80 receives the reflected light to create and stores a reference image. The reference image may be stored in the memory (not shown) provided in the sensor module 80 or in the memory 101 provided in the controller 100. The sensor module 80 receives information stored in the memory 101, which may be used when the displacement of the rotary tub 30 is calculated (200, 210 and 220).

Subsequently, the controller 100 determines whether laundry has been put into the rotary tub 30. The determination as to whether the laundry has been put into the rotary tub 30 may be achieved based on the operation of the door 50, a user command, or a laundry sensor (230).

Upon determining that the laundry has been put into the rotary tub 30, the controller 100 transmits a control signal to the sensor module 80 to detect a current image pattern of at least one side of the rotary tub 30. Upon receiving the control signal from the controller 100, the sensor module 80 irradiates light to at least one side of the rotary tub 30 (240).

When the light irradiated to the rotary tub 30 is reflected, the sensor module 80 receives the reflected light to detect and store a current image. The current image is stored in the memory (not shown) provided in the sensor module 80 or in the memory 101 provided in the controller 100. The sensor module 80 receives information stored in the memory 101, which may be used when the displacement of the rotary tub 30 is calculated (250 and 260).

Subsequently, the sensor module 80 compares the current image with the reference image to sense image change. The sensor module 80 compares the current image with the reference image to detect coordinate change with respect to a predetermined region (a region at which the mask window is set) and to calculate the displacement of the rotary tub 30 based on the coordinate change (270).

Subsequently, the controller 100 retrieves the weight of laundry corresponding to the displacement of the rotary tub 30 transmitted from the sensor module 80 from the memory 101 to calculate the weight of the laundry (280).

FIG. 11 is a control flow chart illustrating a method of measuring the amount of light reflected from the rotary tub to sense the weight of laundry according to an embodiment.

Before laundry is put into the rotary tub 30, the sensor module 80 irradiates light to the rotary tub 30 to measure and store the amount of light reflected from the rotary tub 30 (reference light amount). When the light irradiated to the rotary tub 30 is reflected, the sensor module 80 senses and transmits the reflected light amount to the controller 100. The controller 100 stores the reference light amount in the memory 101 or an external memory (not shown). When the distance between the sensor module 80 and the rotary tub 30 is short, the sensed light amount is increased. When the distance between the sensor module 80 and the rotary tub 30 is long, the sensed light amount is decreased. The light amount sensed without having laundry in the rotary tub 30 is referred to as reference light amount (300, 310 and 320). It is also understood that a reference light amount may be stored when the washing machine is manufactured or can be updated by a user or manufacturer.

Subsequently, the controller 100 determines whether laundry has been put into the rotary tub 30. The determination as to whether the laundry has been put into the rotary tub 30 may be achieved based on the operation of the door 50, a user command, or a laundry sensor (330).

Upon determining that the laundry has been put into the rotary tub 30, the controller 100 transmits a control signal to the sensor module 80 to measure light amount reflected from at least one side of the rotary tub 30. Upon receiving the control signal from the controller 100, the sensor module 80 irradiates light to at least one side of the rotary tub 30 (340).

When the light irradiated to the rotary tub 30 is reflected, the sensor module 80 receives the reflected light to sense light amount. The current light amount measured after laundry is put into the rotary tub 30 is stored in the memory 101 provided in the controller 100 or in an external memory (not shown) such that the controller 100 uses the stored current light amount when calculating light amount change due to the displacement of the rotary tub 30 (350).

Subsequently, the controller 100 compares the current light amount with the reference light amount to sense light amount change and calculates the weight of laundry corresponding to the light amount change (360 and 370).

As is apparent from the above description, the displacement of the rotary tub into which laundry is directly put is detected to confirm the weight of the laundry, thereby improving accuracy in detecting the weight of the laundry.

Although a few embodiments have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit thereof, the scope of which is defined in the claims and their equivalents. 

1. A washing machine, comprising: a rotary tub displaced according to weight of laundry; at least one sensor module to detect displacement of the rotary tub; and a controller to calculate the weight of the laundry according to the displacement of the rotary tub.
 2. The washing machine according to claim 1, further comprising: a water tub in which the rotary tub is provided, wherein the sensor module is mounted at a front upper end of the water tub inside the water tub.
 3. The washing machine according to claim 1, further comprising: a water tub in which the rotary tub is provided, wherein the sensor module is mounted at a rear upper end of the water tub inside the water tub.
 4. The washing machine according to claim 1, wherein the sensor module comprises a light source to irradiate light to the rotary tub and an image sensor to receive the irradiated light to sense an image.
 5. The washing machine according to claim 4, wherein the sensor module further comprises an image processor to detect displacement of the rotary tub according to the image sensed by the image sensor.
 6. The washing machine according to claim 4, wherein the image has a pattern.
 7. The washing machine according to claim 5, wherein the image sensor senses an images of one side of the rotary tub when laundry is in the rotary tub, and the image processor compares the sensed image with a reference image to detect the displacement of the rotary tub.
 8. The washing machine according to claim 1, wherein the sensor module comprises a plurality of sensor modules mounted at a water tub in which the rotary tub is provided, and the controller averages or sums displacements of the rotary tubs detected by the sensor modules to calculate the weight of the laundry.
 9. The washing machine according to claim 1, wherein the sensor module comprises a light emitting part to irradiate light to the rotary tub and a light receiving part to receive light reflected from the rotary tub.
 10. The washing machine according to claim 9, wherein the sensor module irradiates light to the rotary tub and receives light reflected from the rotary tub before and after the laundry is put into the rotary tub.
 11. The washing machine according to claim 10, wherein the controller compares light amounts received before and after the laundry is put into the rotary tub to calculate the weight of the laundry.
 12. The washing machine according to claim 7, wherein the reference image sensed without having laundry in the rotary tub.
 13. The washing machine according to claim 1, further comprising: a memory to store the weight of the laundry according to the displacement of the rotary tub, wherein the controller receives information on the weight of the laundry according to the displacement of the rotary tub from the memory to calculate the weight of the laundry.
 14. A control method of a washing machine, comprising: irradiating light to a rotary tub which is displaced according to weight of laundry; receiving light reflected from the rotary tub to detect displacement of the rotary tub; and calculating the weight of the laundry according to the displacement of the rotary tub.
 15. The control method according to claim 14, wherein irradiating light to a rotary tub which is displaced according to weight of laundry comprises irradiating light to the rotary tub before and after the laundry is put into the rotary tub.
 16. The control method according to claim 15, wherein receiving light reflected from the rotary tub to detect displacement of the rotary tub comprises receiving light reflected from the rotary tub when the laundry is put into the rotary tub to detect an image of the rotary tub and comparing the images of the rotary tub when the laundry is in the rotary tub with a reference image to detect the displacement of the rotary tub.
 17. The control method according to claim 16, wherein the reference image detected without having laundry in the rotary tub.
 18. The control method according to claim 15, wherein receiving light reflected from the rotary tub to detect displacement of the rotary tub comprises measuring light amounts reflected from the rotary tub when the laundry is in the rotary tub and comparing the light with a reference light amount to detect the displacement of the rotary tub.
 19. The control method according to claim 18, wherein the reference light amount is detected without having laundry in the rotary tub. 